165 9 response shift.13 Survivors may have adapted to their new health situation and experience a change in their frame of reference, which may affect QoL outcomes.14 Besides, most cognitive function studies in patients with cancer find that self-reported outcome measures correlate more strongly with factors such as depression, fatigue and anxiety than with objective measures.1 Patients could also be biased by the explanation of their doctor about a certain treatment. For example, when they are being told to undergo proton- instead of photon treatment because of the lower complication possibility, patients might be more likely to rate their symptoms to be lower. In addition, PROMs are often long and thus time consuming. These items describe the complexity of PROs. Future research should discuss the preferred and most important outcome, which influences the type of measurement you should use. When recording a patient’s experience, PROs should be measured. When recording whether a type of treatment resulted in an actual change in outcome, objective measures should be used. In order to create the overall picture of a patients’ performance and develop strategies to reduce side-effects of oncological treatment, it is important to measure both the patient’s evaluation of his or her oral functioning and the objective function of the various organs involved. In this way, objective tests are an addition to PROs, which will lead to creating the complete picture of a patient’s functioning and wellbeing. As found in the associative models for the objective tests in chapter 6 and 7, and for the SWAL-QOL questionnaire in chapter 8, different factors are of importance for the outcome measure. Preferably, in the future, all objective tests and PROs can be combined into one overall score, to predict the patients at risk for developing food processing and swallowing problems after HNC treatment. A possible improvement in future research could be to assess how PROs and objective measures co-vary across time.1 Instead of looking at the correlation between PROs and objective measures at a given time point, an improvement could be to look at the changes in a PRO or objective measure between different time points and compare the fluctuation over time between PROs and objective measures. In addition, a more uniform way of reporting results should be used. Chapter 2describes a review measuring PROs regarding mastication in patients with oral cancer. There was a large variety in the way PROs were presented. In addition, different subgroups of patients were measured, as the tumor subsite in the oral cavity, treatment, and timing of assessment differed in all studies. Multiple studies performed a cross-sectional study, making it impossible to investigate changes over time. Future research should therefore assess patients at multiple points in time to be able to compare PROs and tell something about the impact of, e.g., a certain treatment on QoL. In addition, a uniform way of reporting results should be used when presenting PROs, preferably with the help of guidelines and the use of validated PROs.15
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